A control apparatus for a fluid flow apparatus driven by a motor for feeding a fluid from an inlet and letting the fluid flow out from an outlet is conventionally known. For example, a control apparatus provided in a fuel cell system is conventionally known.
JP2004-95226A (document 1), proposing a fuel cell system, describes an example of such control apparatus. According to this document, the fuel cell system includes an oxidative gas-supplying apparatus (compressor) 5 for supplying an oxidative gas to the fuel cell body 6, an oxidative gas-flux sensor 7 for detecting a flux of the oxidative gas supplied from the oxidative gas-supplying apparatus 5 to the fuel cell 6, a current sensor 8 for detecting an output current from the fuel cell 6, and a controller 15 for controlling the flux of the fuel gas and the oxidative gas. In the fuel cell system, in a normal state, the flux of the oxidative gas is controlled with high accuracy by feedback controls utilizing a detected value of oxidative gas flux QS detected by the oxidative gas-flux sensor 7. In contrast, in an abnormal state, in which the detected value of the oxidative gas-flux sensor 7 deviates from a normal range determined on the basis of operation conditions of the fuel cell, the flux of the oxidative gas is controlled by a feed forward control, being switched from the feedback control.
A target air flux-calculating portion 23 calculates a target air flux on the basis of a required amount of electricity generation. An estimated air flux-calculating portion 24 calculates an estimated air flux on the basis of a current of generated electricity of the fuel cell 6 detected by the current sensor 8. An air flux sensor-normal range-calculating portion 25 calculates a normal range of the detected value detected by the air flux sensor 7, utilizing the estimated air flux calculated by the estimated air flux-calculating portion 24, on the basis of operation conditions of the fuel cell. An air flux sensor-monitoring portion 26 monitors whether the detected value detected by the air flux sensor 7 is within the normal range or not. A feed forward (FF) control portion 27 calculates, on the basis of the target air flux QE calculated by the target air flux-calculating portion 23, with referencing control maps or the like recorded in advance, a command value of rotational speed of the compressor 5 during the feed forward control. A feedback (FB) control portion 28 calculates, on the basis of the target air flux QE calculated by the target air flux-calculating portion 23 and the detected value of the air flux detected by the air flux sensor 7, a command value of rotational speed [rpm] of the compressor 5 during the feedback control.
JP2004-213945A (document 2), proposing a fuel cell system, describes another example of a control apparatus. As described in the document, a fuel cell system 10 includes a fuel cell 12 and a reformer 14. For supplying a fuel gas, air, and/or purified water to the fuel cell 12 and the reformer 14, pumps (or blowers, motors) 16a to 16c, 18a and 18b, 24a and 24b are provided. These pumps are controlled by a computer (not illustrated), utilizing a feedback control for controlling the flux. In other words, each pump includes a sensor (not illustrated) for detecting the flux of each pump. The flux detected by each sensor is fed back to the computer. The computer transmits, for example, a value for pulse width modulation (PWM value) to the pumps and/or motors so that each flux becomes the target value. For the feedback control, a control output value, for example, a value for a pulse width modulation (PWM value), is transmitted to each pump (supplying apparatus). On the basis of the control output value, a time until the supplying apparatus will become uncontrollable is calculated. Then, a rest lifetime in which the supplying apparatus is controllable is calculated. When the rest lifetime becomes larger than a set rest lifetime, the computer gives an alarm.
Further, JP2000-163134A (document 3), proposing a flux control valve and a fuel cell system, describes another example of a control apparatus. As described in the document, a flux control valve provided in a fuel cell system includes a temperature detecting means 104 (temperature sensor 3) for detecting a temperature of a fluid, a pressure detecting means 101 (pressure sensor 4) for detecting a pressure of the fluid, a pressure difference detecting means 102 (pressure difference sensor 5) for detecting a difference between pressures at a first side port and a second side port, a means 108 (motor 6) for controlling a degree of opening of the valve, a means 103 (sensor for detecting a degree of opening 20) for detecting a degree of opening of the valve, a means 105 for calculating an amount of mass flow of the fluid on the basis of the detected pressure, the detected pressure difference, and the detected degree of opening, and a means 107 for repeatedly performing the control and calculation so that the calculated mass flow becomes a set value. The means 105 for calculation calculates an effective cross-sectional area S of the valve on the basis of a pressure P2 at the second side port, a pressure difference ΔP between a pressure at the first side port and the second side port, and the degree of opening, utilizing a map data stored in a read only memory (ROM). Then, the means 105 for calculation calculates a mass flow of air on the basis of the calculated effective cross-sectional area S of the valve, the pressure P2 at the second side port, the pressure difference ΔP between pressures at the first side port and the second side port, and a density σ of the fluid, utilizing equations 1 and 2 described in the document 3.
In the fuel cell described in the document 1, in a normal state, the compressor 5 is controlled by the feedback control, utilizing the detected value of the oxidative gas flux QS detected by the oxidative gas-flux sensor 7. In an abnormal state, the oxidative gas flux is controlled by the feed forward control on the basis of the target air flux QE calculated by the target air flux-calculating portion 23 on the basis of the required amount of electricity generation, referencing a control map or the like stored in advance. In such a feedback control, because a flux sensor is required, an apparatus tends to become large in size, and high in cost. In addition, in the feed forward control, because the command value of the rotational speed is calculated on the basis of only the target air flux QE, there is a danger that the command value of the rotational speed becomes inaccurate, and a desired oxidative gas flux cannot be supplied with high accuracy.
In the fuel cell described in the document 2, the pumps are controlled by the feedback control, utilizing detected results detected by the sensor for detecting the flux. Accordingly, similarly to the document 1, because the flux sensor is required, an apparatus tends to become large in size, and high in cost.
In the flux control valve and the fuel cell system described in the document 3, the mass flux of the fluid is calculated on the basis of the detected pressure, the detected pressure difference, and the detected degree of opening without utilizing costly mass flow meter. The flux is thus controlled accurately. The mass flux of the fluid is calculated as follows. Firstly, the effective cross-sectional area S of the valve is calculated on the basis of the pressure P2 at the second side port, the difference ΔP between pressures at the first side port and the second side port, and the detected degree of opening, referencing the map data stored in the ROM. Then, the mass flux of air is calculated on the basis of the calculated effective cross-sectional area S of the valve, the pressure P2 at the second side port, the difference ΔP between pressures at the first side port and the second side port, and the density σ of the fluid, utilizing equations 1 and 2 described in the document 3. This method for calculating the mass flux can be efficiently applied to a flux control valve. However, this method may not be efficiently applied to a fluid flow apparatus.
A need thus exists for a fluid flow control apparatus which enables to control a flux of a fluid with high accuracy without utilizing high-cost and large-size mass flow meter, and a fuel cell system including the fluid flow control apparatus. The present invention has been made in view of the above circumstances and provides such a control apparatus for a fluid flow apparatus and such a fuel cell system.